There are many processes for converting biomass into useful products, such as fermentable sugars and other chemicals. Some of these biomass conversion processes require pumping biomass slurries to high pressures, such as about 500 psi to about 4000 psi or even higher. Processing biomass slurries at higher solids contents is more economical, because higher solids contents provide a higher output for a given plant size, as well as a lower processing cost, such as in heating, cooling, and concentration costs, because there is less water present. However, high solids content slurries typically are thick and viscous, and therefore are difficult, or sometimes impossible, to pump efficiently or effectively using conventional methods.
There are a limited number of high pressure pump technologies that can pump high solids content slurries to high pressure. These limitations are further exacerbated by the need for the pumps to handle high solids content slurries, which typically have high viscosities. Some have attempted to address these shortcomings by preheating the high solids content slurries in indirect contact heat exchangers. However, this solution often leads to fouling of the heater exchangers, thereby lowering operability, and has high attendant capital costs for the equipment. Furthermore, it is difficult to maintain a uniform temperature within the slurry in the heat exchangers. In addition, there is a significant pressure drop across the heat exchangers, which requires additional pumping power in an already difficult application.
Thus, there is an ongoing need for methods for pumping slurries to high pressures, especially for slurries having high solids contents or high viscosities. The methods of the present invention are directed toward these, as well as other, important ends.